This invention relates to a method for producing filament yarns of high strength, high modulus carbon fibers. More particularly, it relates to a method for producing filament yarns of high strength, high modulus carbon fibers by specifying raw materials and spinning condition.
As the result of recent rapid growth of industries for manufacturing aircrafts, motor vehicles and other transport, a demand for materials prepared by a combination of special materials as a material necessary to these industries capable of exhibiting remarkable characteristics because of the superiority of some of their physical properties is ever increasing. Particularly, the demand for the advent of inexpensive materials provided with high strength and high modulus together with lightness of weight is great. However, since the material which satisfies the above-mentioned demand cannot be supplied in a stabilized manner according to the present status of art, research works relative to composite articles (reinforced resins) which meet the above-mentioned requirement are prevailing.
As one of the most promising material to be used as reinforced resin, there can be mentioned high strength, high modulus carbon fibers. These materials have appeared from about the time when the rapid growth of the above-mentioned industry just started. When the carbon fibers are combined with a resin, it is possible to produce reinforced resins capable of exhibiting characteristic feature unparalleled in the past. To be regretful enough, however, in spite of the high strength and high modulus of the carbon fibers for the above-mentioned reinforced resins capable of exhibiting extremely notable characteristic feature, the application fields of these fibers have not expanded. The cause of this fact, as explained later, lies in the higher production cost.
It is well known that the materials for high strength, high modulus carbon fibers which are commercially available are mostly polyacrylonitrile fibers produced by a special production process and a special spinning process but these acrylonitrile fibers are not only expensive as a precursor of carbon fibers but also the production yield thereof from the precursor is as low as less than 45%. These facts complicate the treatment steps and enlarge production facilities for producing superior carbon fibers, resulting in the increasing production cost of the ultimate products of carbon fibers. The production cost of high strength, high modulus carbon fibers of the ultimate product is further increased by the treatment cost, etc. of hydrocyanic acid by-produced at the time of carbonization treatment.
As for one method for producing high strength, high modulus carbon fibers at a low cost, there are descriptions in the official gazette of Japanese patent publication No.1810 (1979) issued to Union Carbide Corporation and it is a well known fact that mesophase-containing pitches are extremely superior raw material as raw materials for filament yarns of high strength high modulus carbon fibers. For pitches as raw materials of high strength, high modulus carbon fibers, the content of mesophase and the physical properties of mesophase itself naturally give large influence upon the physical properties of carbon fibers. The higher the mesophase content and the better the quality of mesophase, the greater the improvement of the physical properties of carbon fibers.
However, the carbon fibers produced from a 100% mesophase, as a raw material, through a melt-spinning process by using nozzles having a circular cross-section, followed by the steps of thermosetting and carbonization, show radial arrangement of carbon in the cross-section of carbon fibers and create cracks. Thus the resultant carbon fibers have little value as articles of commerce.
Accordingly, it is an object of the present invention to provide a method for producing high strength, high modulus carbon fibers having no drawbacks of conventional carbon fibers prepared according to conventional technique as above-mentioned but having sufficient value as articles of commerce.